The present invention relates to an actuating system for a cascade-type thrust reverser in which the torque or moment forces exerted on the cowling by the linear actuator are minimized, or eliminated altogether.
Turbofan-type turbojet engines are well known in the art and typically comprise a fan located at the front of the turbojet engine, which fan directs a flow of bypass air through a duct bounded by an engine cowling on the inside and a fan cowling on the outside. The generally annular duct bounded by the engine cowling and the fan cowling may channel both the bypass flow and the primary exhaust flow at a downstream portion of the turbojet engine, or the duct may channel only the bypass flow. In aircraft in which the engine is mounted outside of the airframe structure, the fan cowling is configured to provide an aerodynamic outer surface to reduce drag.
Various types of thrust reversers may be utilized with the fan cowling to provide the necessary thrust reversing forces. A cascade thrust reverser is among the known types and is illustrated in FIG. 1. A thrust reverser panel 7 is affixed to the engine structure so as to be movable with respect to the fan cowling 5. In a forward thrust position, illustrated in FIG. 1, the thrust reverser panel 7 covers a reverse thrust opening formed in the cowling such that the gases are directed in a forward thrust position through the annular duct 17 bounded on the outside by the fan cowling and thrust reverser panel 7, and on the inside by the jet engine cowling 16. Thrust reverser flap 12 is pivotally attached to the thrust reverser panel 7 and is also pivotally attached to the engine cowling 16 by linkrod 14 and pivot 15. In known fashion, as the thrust reverser panel 7 moves rearwardly (towards the right as viewed in FIG. 1), the flap 12 pivots inwardly so as to substantially block the annular flow duct 17 and to force the gases outwardly through the cowling across the thrust reversing cascades 13.
Displacement of the thrust reverser panel 7 between the forward and reverse thrust positions is achieved by linear actuator 4. Linear actuator 4 typically comprises a cylinder having an extendable and retractable rod with the cylinder being fixedly attached to and extending through the cowling frame 6, while the distal end of the rod is connected to the thrust reverser panel 7 at pivot 9. Typical, known thrust reversers of this type are illustrated in European Patent 0 109 219 and U.S. Pat. No. 3,500,645.
While generally successful, these known thrust reversers have created some problems. Specifically, the rigid attachment of the linear actuator 4 to the cowling frame 6 is radially displaced from the engagement of flange 3, formed on the cowling frame 6, with a groove formed in the cowling structure 5 by a distance L1. During actuation of the thrust reverser, forces F1 exerted on the cowling frame 6 by the linear actuator 4 generate a torque or moment M1 about the engagement of the flange 3 with the groove formed in the cowling structure 5. Since the thrust reverser panel 7 moves axially relative to the cowling, the linear actuators 4 are also oriented substantially parallel to the longitudinal axis of the cowling necessitating their attachment to the cowling frame 6 at a location displaced radially outwardly from the engagement of the flange 3 with the groove formed in the cowling structure 5. This positioning is also required since the linear actuator is attached to the thrust reverser panel 7 in a portion where the overall radially oriented thickness of the panel 7 is reduced. The connection 9 is located at a radial location of the convex streamlines of the gas flow.
The flaps 12 are covered by an inner portion of the thrust reverser panel 7 and a lower portion of the cowling frame 6. The cowling frame 6 is shaped to absorb the aerodynamic stresses acting on the thrust reverser structure during thrust reverser actuation. The structural requirements of the cowling frame 6 generally preclude mounting the linear actuator 4 in a more radially inward position.
This location of the linear actuator 4 also places part of the actuator, along with the associated hydraulic plumbing connected to the actuator, forwardly of the cowling frame 6. Usually this forward area is a designated fire zone and extra precautions must be taken to insure that no leakage of hydraulic fluid, which is flammable, can take place.
Another problem is caused by the location of the cascades 13 radially outwardly of the flange 3. Such a location increases the torque or moment acting on the cowling frame 6, since the resultant of the thrust reversing forces transferred to the cowling frame 6 by the cascades 13 during thrust reversal increase the torque or moment M1, thereby requiring the cowling frame 6 to be structurally reinforced.